This invention relates to optically based machine vision techniques, and more particularly to techniques for determining the three-dimensional coordinate geometry of certain types of scanned surfaces where the subject is largely comprised of more gently changing surfaces, such as animal and human surface anatomy.
Optically based machine vision systems, when used for the purpose of mapping the geometry of a surface, typically use one or more of either electronic cameras or input perspectives (using mirrors) in order to create a difference in viewing angle for the scanned subject. In order to generate these multiple perspectives, structured light beams typically in the shape of a line, would be moved over the surface with a series of images being simultaneously captured by the machine vision system""s cameras. These multiple perspectives allow the various optical machine vision systems to first correlate common points of reference on the scanned subject""s contours, and then to utilize algorithms which triangulate on these points so as to eventually transform them into three-dimensional coordinate measurements.
Thus what begins as a two-dimensional graphics image comprised of camera-image pixels (as originally scanned or captured through the machine vision cameras) is transformed into a three-dimensional surface definition of the subject""s geometry, or contour map. Accomplishing the creation of this resultant database of surface coordinates allows the surface to be utilized in a wide variety of purposes and manners, not least of which would include Computer Aided Design and Computer Aided Manufacture (CAD/CAM) processes and products. The accuracy and resolution by which the coordinate database describes the original surface of the subject scanned is related in part to both the density with which these common points are selected and measured upon the surface of the subject, as well as the extent to which the entire surface of the subject has its contour mapped with these points of measurement. Generally speaking, the more of these common points which are identified and measured over the greatest extent of the surface possible, the more completely, accurately and precisely the surface contours of the original subject are defined.
Depending upon the particular types of application, varying amounts of the original subject""s surface need to be scanned so that they might be reduced to the desired coordinate geometry definition. As an example, it is desirable when foot anatomy is scanned for the purpose of producing a foot orthosis, that the side dimensions of the foot (including the side of the medial arch, the lateral side, and the back of the heel areas) should be measured, along with the contours of the underside of the foot; however the top of the foot is irrelevant. Since at least two input perspectives must normally be acquired in order to triangulate on any one point of the surface""s contours (and thereby derive a three-dimensional coordinate measurement for that point), this has typically been achieved by adding more expensive equipment, including greater numbers of viewing components such as cameras or mirrors, more light sources, lenses and other optical components, machine extensions, larger enclosures and moving or motorized parts, etc. Additionally, more camera images are typically taken, with the overall effect of the foregoing problems typically resulting in a bulkier, more costly, and usually slower operating machine. This slowness in executing a scan was generally required by the design approach of using moving parts or extensive sequences of camera images.
In accordance with an aspect of the invention, a method is described for optically scanning a subject having a three-dimensional surface contour, comprising:
illuminating the subject with a matrix of discrete two-dimensional image objects;
capturing respective object illumination images of the illuminated subject from different known image perspectives; and
processing the respective object illumination images to obtain a set of three-dimensional coordinates of at least a portion of the surface contour, said processing including correlating positions of common discrete image objects in the respective illumination images, using data regarding the image perspectives.
In accordance with another aspect of the invention, a machine vision system is disclosed, and includes camera apparatus disposed at different camera perspectives relative to a subject, and one or more light projectors for projecting a grid-like structured light projection onto the subject. The machine vision system captures a sequence of images including a light object projector image and an ambient light reference image from each camera perspective. A processor determines and correlates the image light objects to generate a set of common surface reference points between camera perspectives, and then triangulates upon the reference points to produce a three-dimensional set of coordinates for at least a portion of the surface of the subject.